A new detector has a clever way of detecting dark matter

Liquid on the verge of boiling bubbles with the slightest nudge of dark matter.

A new dark matter detector has gone online today, using a rather clever method of searching for signs of rare interactions between dark and regular matter. The tool uses a liquid that's kept poised on the edge of boiling, such that even the tiniest bit of additional energy—say, caused by the impact of a dark matter particle—will create a bubble of vapor in the detector.

The new detector is called COUPP, for Chicagoland Observatory for Underground Particle Physics. Although it was organized by Fermilab outside of Chicago, the detector resides in Canada's SNOLAB, deep in a mine near Sudbury, Ontario. This location shields it from a lot of the background noise of particles that come from the atmosphere and radioactive substances.

The idea behind the detector is similar to that of the CDMS experiment. Most evidence points to dark matter being composed of WIMPS—weakly interacting massive particles. Although dark matter mostly interacts with other matter via gravity, in some models there's a chance that it can physically interact with regular matter, albeit very weakly. To search for these interactions, researchers must detect collisions that only impart a tiny bit of energy to a material.

In CDMS, they do so by keeping the atoms of their detectors just above absolute zero, so any additional energy should stand out. COUPP uses a rather different approach. It starts with a pool of a heavy liquid—a mixture of water and trifluoroiodomethane, which is a single carbon linked to three fluorines and an iodine. It then holds that liquid right at its boiling point and adds enough energy so that it's poised to undergo a transition to a vapor with the slightest addition of energy. When a dark matter particle bumps into an atom and adds some energy, a small bubble of vapor briefly appears in the liquid. Most of the potential background events are much more energetic, and they will leave a trail of bubbles through the detector.

In some ways, the detector is reminiscent of the bubble chambers that were once used to track events in particle colliders. But the actual setup is quite different, and the WIMPs they're searching for have so far eluded even the most advanced particle detectors.

Can and will. Just like CDMS and other Dark Matter experiments (or all particle experiments, really) they'll have to look at their measured events and see if they look like neutrinos, another known particle, or something new. And then they'll have to see if it fits within the constraints established by other observations for the possible characteristics of Dark Matter (though "something new" would be fantastic even if it doesn't match with DM observations).

Can and will. Just like CDMS and other Dark Matter experiments (or all particle experiments, really) they'll have to look at their measured events and see if they look like neutrinos, another known particle, or something new. And then they'll have to see if it fits within the constraints established by other observations for the possible characteristics of Dark Matter (though "something new" would be fantastic even if it doesn't match with DM observations).

To be a bit more specific: neutrinos have a mass of around 1 eV (they don't really know, 2.2 is the upper limit). The WIMPs they are looking for have a mass of around 10-10000 GeV.

Neutrons are actually by far the biggest problem, as they have a mass of nearly 1GeV, which is pretty close (in these kinds of physics) to that of the WIMPs. It's not really possible to distinguish neutron impacts from dark matter impacts in a single event: they use a combination of shielding and statistics to eliminate as many of them as they can. Thats one reason why this new detector has so much potential: since neutrons won't just cause one impact, while WIMPs will, they can rule out events that cause multiple bubbles in the detector.

The other advantage is scale. You can make multi-tonne detectors by simply building a bigger tub, and the materials are fairly cheap. The CDMS detectors don't scale well, and are very expensive.

Neutrons are actually by far the biggest problem, as they have a mass of nearly 1GeV, which is pretty close (in these kinds of physics) to that of the WIMPs. It's not really possible to distinguish neutron impacts from dark matter impacts in a single event: they use a combination of shielding and statistics to eliminate as many of them as they can. Thats one reason why this new detector has so much potential: since neutrons won't just cause one impact, while WIMPs will, they can rule out events that cause multiple bubbles in the detector

How many stray neutrons are there in Background radiation? It can't be enough that sufficient shielding would make their presence virtually nil, can it?

To be a bit more specific: neutrinos have a mass of around 1 eV (they don't really know, 2.2 is the upper limit). The WIMPs they are looking for have a mass of around 10-10000 GeV.

Latest astrophysical upper limits are less than 1 eV, from what I recall (I work in neutrino physics, but our experiment is not very involved with the masses). There's apparently (from Wikipedia) a lower limit of 0.04 eV from the mass differences themselves.

How many stray neutrons are there in Background radiation? It can't be enough that sufficient shielding would make their presence virtually nil, can it?

Quite a few, actually. There will be neutrons from radioactive decays in the rock around the mine and a number produced by interactions from cosmic-ray-produced muons that penetrated to the experiment and interacted with the materials within it.

I wonder if such a detection system could allow for the discernment of proton decay.

It's much easier to just pile up humongous amounts of water and look for unexpected events. Proton decay isn't really a "thing" anymore anyways; the lower limit is ~10^33 years for the half-life, which is getting a bit impractical to measure in a reasonable amount of time.

I'm always excited to see the results of new experiments like this, especially since the picture painted by the current state of the art cosmology seems a very... odd one.

Sometimes I wonder if we're on the verge of discovering solid evidence that our world is a (flawed) simulation. Maybe all this dark energy and quantum entanglement are just simplifications like the population fudging in Sim City 5! Or perhaps we're simply chasing phantoms and dark matter is really like luminiferous ether, a wild goose chase waiting for more evidence to show the more elegant reality.

How many stray neutrons are there in Background radiation? It can't be enough that sufficient shielding would make their presence virtually nil, can it?

Depends a lot on the environment. It says that the facility is in a mine in Canada and, while I'm not familiar with this particular mine, there is a lot of uranium dug up in Canada. Large amounts of uranium could easily produce significant (for this experiment) levels of background neutrons. See also the comment about cosmic rays above.

The problem with sheilding and detecting is that you are alsways working against your own interests. In this case you can probably get away with a bit of sheilding since neutrons will be stopped by low Z materials while the WIMPS will not.

I'm always excited to see the results of new experiments like this, especially since the picture painted by the current state of the art cosmology seems a very... odd one.

Sometimes I wonder if we're on the verge of discovering solid evidence that our world is a (flawed) simulation. Maybe all this dark energy and quantum entanglement are just simplifications like the population fudging in Sim City 5! Or perhaps we're simply chasing phantoms and dark matter is really like luminiferous ether, a wild goose chase waiting for more evidence to show the more elegant reality.

How do the sensors see the bubbles? It seems any sort of detection device would add energy to the system.

I am sure they use a CCD camera.

So yes, there will be vast numbers of photons illuminating the chamber, and some of them will be absorbed. Perhaps this is part of the background and/or the 1-2 eV that a photon gives just isn't enough to start a bubble.

And they will make sure not too many photons are absorbed: i.e. they make sure the liquid is transparent at to whatever colour of light they use. Think about optical fibre, they can get photons to go through 50km of glass!.

How many stray neutrons are there in Background radiation? It can't be enough that sufficient shielding would make their presence virtually nil, can it?

Derp-edit: I read neutrons as neutrinos. Oh well,

As you read this sentence, trillions and trillions of neutrinos are passing through your eyeball. Maybe one or two will interact with your tissue in a year.

There's really no such thing as shielding for neutrinos. To cut the neutrino background by just 50% with a shield made of lead, that shield would have to be one light year thick.

Neutrino interactions are very rare, which makes detecting them above other vastly more common sources of background noise is difficult. So for example the Ice Cube neutrino telescope takes advantage of the neutrino's tendency to pass through everything and specifically looks for events that came from beneath it -- as in neutrinos that passed all the way through the planet earth before reaching their detectors. The planet earth makes an exceptionally good filter for non-neutrino cosmic rays, while being essentially transparent to the neutrinos themselves.

Dark Matter is expected to interact even more rarely than neutrinos. Which makes detecting it above background noise -- which now includes neutrinos -- even more difficult.

These fine folk seem to have come up with a very clever detection method that may actually make it much easier to sort out.

Sometimes I wonder if we're on the verge of discovering solid evidence that our world is a (flawed) simulation. Maybe all this dark energy and quantum entanglement are just simplifications like the population fudging in Sim City 5! Or perhaps we're simply chasing phantoms and dark matter is really like luminiferous ether, a wild goose chase waiting for more evidence to show the more elegant reality.

How many stray neutrons are there in Background radiation? It can't be enough that sufficient shielding would make their presence virtually nil, can it?

Depends a lot on the environment. It says that the facility is in a mine in Canada and, while I'm not familiar with this particular mine, there is a lot of uranium dug up in Canada. Large amounts of uranium could easily produce significant (for this experiment) levels of background neutrons. See also the comment about cosmic rays above.

The problem with sheilding and detecting is that you are alsways working against your own interests. In this case you can probably get away with a bit of sheilding since neutrons will be stopped by low Z materials while the WIMPS will not.

I'm always excited to see the results of new experiments like this, especially since the picture painted by the current state of the art cosmology seems a very... odd one.

Sometimes I wonder if we're on the verge of discovering solid evidence that our world is a (flawed) simulation. Maybe all this dark energy and quantum entanglement are just simplifications like the population fudging in Sim City 5! Or perhaps we're simply chasing phantoms and dark matter is really like luminiferous ether, a wild goose chase waiting for more evidence to show the more elegant reality.

How in the world would the Principle of Least Action preclude our world being a simulation? If anything, Least Action is a good intuitive argument for things like the Many Worlds Interpretation, which doesn't seem to preclude anything other than that any such simulator couldn't be constrained by the same computational limits we are. But since it isn't in the simulated universe by definition, why would it be bound by limits on the power of computers in the simulation?

The problem with the hunt for "dark matter" that it's 100% theoretical and not needed to explain the universe. Dark Matter is needed to plug holes in the popular standard model. There are other models of the universe that better reflect the body of observational data we have and have been used to predict discoveries. Something the popular standard model hasn't been able to do.

How do the sensors see the bubbles? It seems any sort of detection device would add energy to the system.

As adrian.ratnapala suspected, they do just use cameras.

The formation of a bubble requires on the order of 1 keV of energy to be deposited very rapidly in a small enough area. Light is not capable of doing this, so light does not trigger events. Neither do other forms of radiation such as gamma and beta radiation: while they can deposit a lot of energy in an event, it is spread out over a large enough region that a bubble does not form.

The problem with the hunt for "dark matter" that it's 100% theoretical and not needed to explain the universe.

Maybe I'm acting too young to understand these attitudes. The current standard cosmology is less odd than the old. And DM is definitely needed:

I have found time to study Susskind's Stanford youtube lectures on cosmology. So far I've run through his newtonian cosmology. It is clear that it sets the basis for the current universe, in that you find yourself studying a spacetime that prefers to be flat, and freewheeling expanding.

And newtonian gravity gives you a fair estimate of age of the universe. In fact Susskind laments that Newton set it up and didn't follow it through, and claims that the age estimate clashed with Newton's young Earth creationist faith.

From that basis the standard cosmology is less odd.

- Inflation prevents, or at least obscures, the need for an initial singularity since it is past-timelike-incomplete. This is no different from quantum field theory doing the same for particles.

It also sets up seed fluctuations for structure. Without them, no structure.

- DM is needed to predict galaxies and stars. Without it you couldn't get from initial fluctuations to what we see, there isn't enough baryonic mass.

- DE is needed to get away from the finetuned balance of a freewheeling universe, it takes care of the fact that gravitation is in fact GR and not newtonian.

Also, DM is 100 % empirical today: the only way to predict the CMB acoustic peaks, its gravitational lensing is seen everywhere and a 10 sigma lensing observation is _from Planck CMB data alone_.

We can't do away with either one any longer, no other theory comes even close.

How in the world would the Principle of Least Action preclude our world being a simulation?

I can't speak for others, but I have seen descriptions of the global extremal seeking nature of least action (and I assume Feynman's path integrals) taken as signs that the universe is not locally algorithmic.

My own intuition is that having quantum mechanics is enough, since it is minimizing both hidden variables (old result: Bell tests) and visible parameters (new result: um, I have that ref somewhere... I hope). If in doubt we should be able to increase detail, say ask for more precision, and a simulation shouldn't be able to keep up as it uses effectively hidden variables and would use more parameters to boot.

Such an analysis would need some quantification from having an observable universe and what computing resources that gives. I'm not sure how to do an estimate, but I'm pretty sure it is doable. It would be a perfect Ars topic perhaps? =D

Some scientists are looking into how to determine if we are just living in a simulation. I personally feel that the Principle of Least Action pretty well precludes it.

The actual problem with the simulation idea is the sheer computational power required to simulate everything. Simulation is more likely than not to resemble the physics of whatever is simulating it, and creating such a simulation is implausible under our laws of physics, ergo, it is unlikely we are in a simulation.

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Maybe I'm acting too young to understand these attitudes. The current standard cosmology is less odd than the old. And DM is definitely needed:

The problem with dark matter is that we have failed to observe the gravitational effects of dark matter locally (i.e. within the distances where we can measure the true locations of objects via parallax) and yet we observe it in extremely large structures (including our own galaxy). The necessary distribution of dark mater to make many observations we have made make sense do not themselves make much sense (for instance, the dark matter distribution of our own galaxy is posited to be a very large ellipsoid, with us being in the narrow equator of the thing)... really, dark matter is basically a "The laws of physics are clearly correct, therefore, dark matter and dark energy must exist." Another possibility is that we are simply wrong about the laws of physics in some major fashion, but whatever mistake we're making is non-obvious. Are our standard candles all wrong? Are we failing to take something basic into account which is throwing off all our results?

Dark matter seems necessary to explain how the universe works but, if dark matter DID exist, it should be all around us and its gravitational effects, at least, should be obvious locally. But they aren't. Which raises all sorts of questions.

The problem with dark matter is that we have failed to observe the gravitational effects of dark matter locally (i.e. within the distances where we can measure the true locations of objects via parallax) and yet we observe it in extremely large structures (including our own galaxy).

Which is to be expected when dealing with something as diffuse as Dark Matter -- e.g. the amount of Dark Matter in the solar system is predicted to be on the order of the mass of Mt. Everest, only evenly distributed. A piddling trifle that would not have any obvious -- or for that matter measurable -- effect.

This is why it only appears relevant on the scale of galaxies or larger, as that's where enough of it adds up over distances much larger than the visible galaxy to make a difference.

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really, dark matter is basically a "The laws of physics are clearly correct, therefore, dark matter and dark energy must exist."

Another way to put it would be that the known laws of physics predict that there is mass in places where we can't see any mass. Since these laws of physics are extremely good at making predictions (see: pulsar binary story here on Ars), we take this prediction seriously.

The possibility that the theory is wrong is of course considered, but it's not only not obvious where our error might be, it's mind-bogglingly hard to explain even if you decide to start with a clean slate. How do you get gravitational attraction towards locations with no mass-energy at all, yet remain consistent with every other observation that gravity does indeed attract masses?

These aren't things that can be got around even assuming the cosmic distance ladder is completely broken.

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Dark matter resembles epicycles in certain unfortunate ways.

Can't think of any relevant ones. The most important aspect of epicycles is that they had zero additional predictive power over ellipses, and deliberately so because they were devised to exactly match ellipses. Dark Matter has substantial additional predictive power (meaning simply that it makes testable predictions that are different than alternative theories), some of which has been dramatically confirmed and which alternatives can't get close to (see: Plank data and power scale of the universe).

To me the historical situations Dark Matter resembles most are the anomalous orbits of Uranus and Mercury. In both cases the orbit did not match our naive calculations, and in both cases Newtonian gravity predicted an additional, unknown mass as the explanation. In one case that prediction was correct and we discovered Neptune, in the other case that prediction was not correct, there was no planet Vulcan, and instead we needed General Relativity to explain it.

The problem with dark matter is that we have failed to observe the gravitational effects of dark matter locally (i.e. within the distances where we can measure the true locations of objects via parallax) and yet we observe it in extremely large structures (including our own galaxy). The necessary distribution of dark mater to make many observations we have made make sense do not themselves make much sense (for instance, the dark matter distribution of our own galaxy is posited to be a very large ellipsoid, with us being in the narrow equator of the thing)...

The gravitational effects of dark matter has been measured on the kpc scale, using the motion of stars based upon parallax. Also, yes, the dark matter distribution is probably ellipsoidal, but much closer to a sphere in shape than some very elongated object. I am not sure where you get the idea it is otherwise.

How in the world would the Principle of Least Action preclude our world being a simulation?

I can't speak for others, but I have seen descriptions of the global extremal seeking nature of least action (and I assume Feynman's path integrals) taken as signs that the universe is not locally algorithmic.

My own intuition is that having quantum mechanics is enough, since it is minimizing both hidden variables (old result: Bell tests) and visible parameters (new result: um, I have that ref somewhere... I hope). If in doubt we should be able to increase detail, say ask for more precision, and a simulation shouldn't be able to keep up as it uses effectively hidden variables and would use more parameters to boot.

Such an analysis would need some quantification from having an observable universe and what computing resources that gives. I'm not sure how to do an estimate, but I'm pretty sure it is doable. It would be a perfect Ars topic perhaps? =D

Well, this seems the right spot for a little wild speculation Yes, the global "pseudo-teleological" properties of things like least-action are extremely interesting, but I think that there are other potential valid explanations. Especially in scenarios like MWI, what we see as teleology-like behavior might be just a kind of post-selection interference between branches of the wave function. For example, with things like a Delayed Choice Quantum Eraser, it appears that a choice later in time can affect the result of a measurement earlier in time, but an alternative viewpoint is that both results occur in different branches of the wave function, and later when you make the decision you always end up in the branch whose history is consistent with that decision.

This I think is philosophically similar to the problems associated with thinking about the Anthropic principle: we have a universe with the constants fixed at livable values because the only consistent history for an observation is a history that allows the existence of observers. Likewise, the future could be essentially selecting from the infinitude of alternative "presents" for one that is consistent with whatever measurements occur in the future. edit: But that wouldn't mean that each possible alternative wouldn't be algorithmically computable; it is just that the post-selection means that most of those branches get thrown away based on future consistency requirements. Of course there is the problem of the infinitude of alternatives... but that's what quantum computation is for.

The problem with the hunt for "dark matter" that it's 100% theoretical and not needed to explain the universe.

......

Maybe I'm acting too young to understand these attitudes. The current standard cosmology is less odd than the old. And DM is definitely needed:

- Inflation prevents, or at least obscures, the need for an initial singularity since it is past-timelike-incomplete. This is no different from quantum field theory doing the same for particles.

We can't do away with either one any longer, no other theory comes even close.

Inflation drives me bonkers. How much of what kind of energy can stretch space time from a tiny thing to billion's of light years in a fraction of a second? Is it possible that the amount of matter and anti-matter were very nearly equal but that on this side of times arrow you have just a very tiny fraction of a percent excess of matter and on the other side of times arrow the opposite? I'm no astrophysicist but obviously some of you are. Are there ANY good concepts as to what drove inflation? Even untestable ones?

How in the world would the Principle of Least Action preclude our world being a simulation?

I can't speak for others, but I have seen descriptions of the global extremal seeking nature of least action (and I assume Feynman's path integrals) taken as signs that the universe is not locally algorithmic.

My own intuition is that having quantum mechanics is enough, since it is minimizing both hidden variables (old result: Bell tests) and visible parameters (new result: um, I have that ref somewhere... I hope). If in doubt we should be able to increase detail, say ask for more precision, and a simulation shouldn't be able to keep up as it uses effectively hidden variables and would use more parameters to boot.

Such an analysis would need some quantification from having an observable universe and what computing resources that gives. I'm not sure how to do an estimate, but I'm pretty sure it is doable. It would be a perfect Ars topic perhaps? =D

The big problem with proving the universe is not a simulation is that we only know what the limitations of simulation would be in our universe. In the meta-universe in which the simulation runs, the rules might all be different.

Inflation drives me bonkers. How much of what kind of energy can stretch space time from a tiny thing to billion's of light years in a fraction of a second?

The same kind of energy as the Higgs possesses, capable of producing enormous masses for point particles at literally all points in space. That adds up, really fast.

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Is it possible that the amount of matter and anti-matter were very nearly equal but that on this side of times arrow you have just a very tiny fraction of a percent excess of matter and on the other side of times arrow the opposite?

If you time reverse the Universe's laws, you get exactly the same Universe with matter swapped out for antimatter. Whether this Universe actually exists is an open question. We simply don't have a theory that operates at energies high enough to say meaningful things about the Big Bang.

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I'm no astrophysicist but obviously some of you are. Are there ANY good concepts as to what drove inflation? Even untestable ones?

Yes. One popular theory that works very well is a scalar field working its way toward a minimum (very much like what the Higgs did). If the value of the scalar's potential starts out very, very large and positive and it takes this scalar a few teensy fractions of a second to work its way to a minimal value, we would observe inflation. It is conceivable that the Planck satellite could pin down the character of the inflation field later this year, which, let's step back for a second, is incredible. By looking at the hundreds-of-thousands-of-years later afterglow, complex assemblies of particles could be about to remember where they came from, gaining real understanding of energies absent from the Universe since its birth, 13.8 billion years later.

Which is to be expected when dealing with something as diffuse as Dark Matter -- e.g. the amount of Dark Matter in the solar system is predicted to be on the order of the mass of Mt. Everest, only evenly distributed. A piddling trifle that would not have any obvious -- or for that matter measurable -- effect.

This is why it only appears relevant on the scale of galaxies or larger, as that's where enough of it adds up over distances much larger than the visible galaxy to make a difference.

The problem is that you're not understanding what I'm talking about. I'm talking about interstellar distances here - all the way out to the maximum measurable distance from parallax (you know, the movement of the earth around the Sun). This is the only region of space in which we can determine absolute velocity and be sure that we are, in fact, correct about it.

On this scale, the effects of dark matter SHOULD BE noticable, because there is a LOT of dark matter which is (supposedly) pulling on it. And yet, we have been unable to observe the pull of dark matter on these stars. That's a bit of a problem, because at such a scale, it DOES have a noticable, measurable impact but it does not seem to be having such an impact. That is a bit of a problem, wouldnt' you say?

Because I think it is.

Now, to be fair, the paper has been complained about by some people, but until someone actually DOES show me that, until someone can show me "Hey look, here it is working in a region of space where we don't have to make a ton of assumptions", I am going to be skeptical. Showing me some distant galaxy being pulled on by dark matter is interesting, but it isn't terribly convincing given that we SHOULD be able to measure its presence locally, and yet have failed to, heretofar.

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Another way to put it would be that the known laws of physics predict that there is mass in places where we can't see any mass. Since these laws of physics are extremely good at making predictions (see: pulsar binary story here on Ars), we take this prediction seriously.

Another way of putting it is that the known laws of physics are failing to predict galactic structure, and we are positing the existence of additional mass in the form of unseeable matter which cannot interact with ordinary matter in order to make our laws of physics align with actual predictions.

And that is the correct way to put it, because that is exactly what is happening. Dark matter is not a prediction; it is a means of making our observations fit with our models. We cannot use dark matter to make predictions.

This does not mean that dark matter doesn't exist, but let's not pretty up dark matter from what it actually is: a means of making our models fit our observations. And that is precisely why it resembles epicycles.

Veritas super omens wrote:

Inflation drives me bonkers. How much of what kind of energy can stretch space time from a tiny thing to billion's of light years in a fraction of a second? Is it possible that the amount of matter and anti-matter were very nearly equal but that on this side of times arrow you have just a very tiny fraction of a percent excess of matter and on the other side of times arrow the opposite? I'm no astrophysicist but obviously some of you are. Are there ANY good concepts as to what drove inflation? Even untestable ones?

There's a Nobel prize in it if you can come up with a good process for it. Mostly right now it is basically speculation. There are some clever ideas, but physicists have clever ideas all the time; most of them are nonsense, of course. Much like "What is dark matter?"

Not to say that they're wrong, just to say, you know, they're unproven, and for the moment, unprovable. Though that could change with future data, just like we COULD discover WIMPs.

I'm not enthused, but I have been wrong before. But I like to think I am merely properly skeptical of grand claims that 95% of the universe is made of dark matter and dark energy.

but until someone actually DOES show me that, until someone can show me "Hey look, here it is working in a region of space where we don't have to make a ton of assumptions", I am going to be skeptical.

Just look at the CMB. The high third peak is a smoking gun. And making our models fit the observations is called science--that's how we are led to dark matter.

The problem is that you're not understanding what I'm talking about. I'm talking about interstellar distances here - all the way out to the maximum measurable distance from parallax (you know, the movement of the earth around the Sun).

Yes, the root of the cosmic distance ladder. The point is that dark matter is actually extremely diffuse and there isn't actually a lot of it compared to normal matter within the visible portion of the galaxy. Sorry that the factoid I had handy to illustrate this was only for the solar system.

Oh and maybe check out the paper already linked for what we can measure.

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Another way of putting it is that the known laws of physics are failing to predict galactic structure... And that is the correct way to put it, because that is exactly what is happening.

Sure, just like it would be correct to have said that about Newton's Law of Gravitation and the orbit of Uranus.

It's also correct to say that if you see a certain kind of motion under the influence of gravity, that General Relativity predicts that there is mass-energy causing that motion. The laws of physics predict mass where the effects of gravity are seen.

Your choice to phrase it the other way is simply reflecting your bias against DM. The "making a prediction" way is neutral scientific phrasing as it naturally allows for that prediction way to be wrong -- and is used even when the prediction is already known to be wrong. There's no need to force needlessly dismissive phrasing if you don't have an axe to grind.

Your implication that General Relativity doesn't actually predict matter based on the observed dynamics is your bias causing you to say thing that are unequivocally wrong.

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We cannot use dark matter to make predictions.

Giant hairy bollocks! There are many predictions that can be made using Dark Matter. One example, we could use it to predict that in some circumstances the Dark Matter and normal matter in a galaxy could become separated, and this has been observed. We could also use it to predict how the large-scale structure formation of the galaxy would be affected, and the observations also match this prediction extremely well; ridiculously well if you compare to the DM-free predictions.

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This does not mean that dark matter doesn't exist, but let's not pretty up dark matter from what it actually is: a means of making our models fit our observations.

Your computer monitor is just a means of making the electromagnetic model match your observation of photons hitting your eyes and normal forces repelling your fingers. You can always flip things around like this, but this is just a semantic game that means nothing.

This doesn't mean dark matter exists. But it is a prediction based on our observations and best theory of gravity. And it could be wrong. There's no reason to try to leverage the negative connotations of words against it.

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And that is precisely why it resembles epicycles.

I don't think you actually understand the reason why a comparison to epicycles is considered a bad thing. Epicycles were a case where, because they were used to explain how you could get ellipses from circles, they was no difference at all, ever between them and actual ellipses. Surely you can see how General Relativity being correct and Dark Matter being real, versus our theory of gravity being wrong, makes a difference in the resulting predictions. Or maybe not? So let's forget DM a second.

Prove me wrong. Show me you understand, by explaining to me how the prediction of Neptune's existence was or was not like epicycles.

Veritas super omens wrote:Are there ANY good concepts as to what drove inflation? Even untestable ones?

Ha.. "untestable"? You got it. Thought nobody ask. I have an "untestable" concept about this inflation, don't know if it sounds any logical to anyone or not.

There was this experiment I had long time ago. I placed a burning match in a large size glass bottle. Closed the cap after.

It took a few seconds for the fire to burn away all the oxygen. When all the oxygen had gone. The bottle became full vacuum.

This effect has a similarity to how our Universe became vacuum after all the oxygen and other elements got burn away. The big question is. Is our Universe inside a sealed bottle? Nothing gets in, and nothing gets out?

With millions of Black Holes and billions of stars burning away the oxygen, hydrogen, helium as well as other elements and get to the point there is no more fresh elements to burn, our Universe will eventually gets under 100 percent full vacuum, just like the bottle did. Maybe not sooner but that date will come, maybe in trillions of trillions of years later? But it will happens.

Is our Universe inside a bottle?

If our Universe is not inside of some sealed containers, how is our Universe stay in vacuum?

And if there is such a container, it must be something made of lead, a glass like material. Something made of high density. If that's the case, our Universe is not a non endless world.

What is this container, if it even exists?

What is it made of?

When all the air eventually had gone away, what will be the pressure of our Universe like? Will it increased to a millionth fold? Will it be a trillion ton per trillionth of a meter? Maybe higher, maybe lower?

A story:

A 5 year old girl was playing in the backyard of her parent's house. She noticed there is a 5 gallon plastic water bottle next to her has become flatter little by little over the last few minutes, and it finally became totally flattened. It's like two piece of flat plastics stack on top of one another. Flattened like it had been run over by an 18 wheeler. That's how flat it was.

She screams to her mom. "Mommy, mommy, something happened to the water bottle."

Mom look out of her kitchen window, "Honey, it's okay. That water bottle is what the Earth people called the Universe. It's because all the air inside of the bottle got burn out by the stars and Black Holes. There's no more air left in there. Honey just unscrewed the cap and let some air gets in, it will be back to its original shape."

The little girl did what her mommy said and unscrewed the cap.

Bang... Fresh air got in once the cap has loosened.

"Mommy, mommy. there's this loud bang from the bottle. It scares me."

"Don't worry honey. The loud bang is what the Earth people called The Big Bang Theory. Ha ha ha.. Those stupid funny Earth people. They need to read up more science articles. It is okay honey, just remember by tomorrow this time, the bottle will gets flattened again, and it repeats it again the day, and after. It will happens once every day. And when it happened, just unscrewed the cap. Oh yeah, honey, just leave the bottle next to the trash can."

Once again our Universe got rejuvenated.

A day of this little girl's time equivalent to trillion of trillion of Earth years.

Fascinating.. right?

Back to the reality: What I believe, and when all the elements burn away by the stars and Black Holes, the pressure will increase. All stars, galaxies will compressed into dust like materials. Some how fresh air got in through some openings at the wall of the Universe because of the high pressure from within, it makes a crack somewhere along the "container". And when that happen, it's like a big bang all over again. The reborn of the Universe. This Big Bang recycles itself once every trillion of trillion of years.

The problem with the hunt for "dark matter" that it's 100% theoretical and not needed to explain the universe. Dark Matter is needed to plug holes in the popular standard model. There are other models of the universe that better reflect the body of observational data we have and have been used to predict discoveries. Something the popular standard model hasn't been able to do.

Actually that's not a very accurate statement. Dark Matter has nothing to do with the Standard Model. In fact DM was first proposed in 1933 by Fritz Zwicky to explain galaxy rotation curves. It has since provided an explanation for the structure of galaxy clusters as well, amongst other things. As for models that "better reflect the body of observational data" there are exactly zero. The delta-CDM inflation model of the Big Bang provides an extremely good fit to observational data at every level, and in fact every new observation since Guth et al first proposed inflation have merely served to strengthen it. There is no other theory which is even remotely in the same league with delta-CDM.

This is fundamentally why most of the physics community has little issue with Dark Matter as a theory. Much like other theories of the past, such as the Atomic Theory of matter, which was accepted on the basis of indirect evidence from chemistry LONG before any direct evidence was presented, or the Newtonian theory of gravity, which posits an invisible force with no perceptible cause acting across an empty vacuum, the theory of Dark Matter is accepted on the basis of indirect evidence. Certainly there are plenty of scientists who would happily replace it with some other theory, but if you actually carefully examine the current Dark Matter theory and the observations it is based on what you find is there's almost no other way left to explain things. Cold heavy WIMPs or something VERY similar are in fact the only proposal which has even come close to being predictive. For all the work that has been done on alternate theories of gravity, etc none of them has ever made even one single accurate prediction, while delta-CDM/WIMPs have made a long list of them.

The problem is that you're not understanding what I'm talking about. I'm talking about interstellar distances here - all the way out to the maximum measurable distance from parallax (you know, the movement of the earth around the Sun). This is the only region of space in which we can determine absolute velocity and be sure that we are, in fact, correct about it.

On this scale, the effects of dark matter SHOULD BE noticable, because there is a LOT of dark matter which is (supposedly) pulling on it. And yet, we have been unable to observe the pull of dark matter on these stars. That's a bit of a problem, because at such a scale, it DOES have a noticable, measurable impact but it does not seem to be having such an impact. That is a bit of a problem, wouldnt' you say?

Citation? I have seen absolutely nothing on this subject. In fact current simulations of the formation and evolution of galaxies indicate that there are discrepencies with observation, but these simulations currently ONLY take into account dark matter, not its interactions with baryonic matter, which are suspected to be significant at galactic scale. Also DM may not be ENTIRELY self-unreactive. A mean path length of something between 1kp and 1mp for non-dissipative interactions between DM particles seems to go a long ways towards explaining things.

As for local effects, I see no indication in the literature that any such effects are considered missing or that there is any anomaly needing to be explained. The distribution of DM in our region of the galaxy would be expected to be both quite even and fairly low in density. Evenly distributed DM simply has no appreciable effects, a fact you can easily corroborate.

So, in fact the situation is that CDM has great explanatory power and within the various limitations on its known characteristics it is quite possible to construct a theory of DM which isn't at odds with existing observations. Constraints however are constantly trightening and we'll see over time how things shape up. Given the high explanatory power of the theory it is seeming less and less likely every year that anything else is going to crop up that can displace it though.

Sure, just like it would be correct to have said that about Newton's Law of Gravitation and the orbit of Uranus.

Yes, except in one case, the laws of gravity were, in fact, actually wrong. The deviation in the orbit of Mercury was due to relativity being a more accurate model of the universe.

When I see a minor deviation from the laws of gravity, I say "There's likely an object sneaking around out there."

When I find out my calculations require me to posit that there is five times as much matter as is visible, I have to question my calculations.

That relativity is correct on objects the size of the solar system is irrefutable. We see a ridiculous amount of evidence suggesting that our laws on such "small scale" things as solar systems is correct, or even local interstellar space. However, when we go up to the size of galaxies, things go crazy, and when we go up into the Hubble Bubble, things get MORE crazy.

Its not at all unreasonable to suggest that the reason that large-scale structures deviate is that we're wrong about gravity, given that on the broadest scale we have to assume that 95% of the universe is only detectable in an indirect fashion.

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Your choice to phrase it the other way is simply reflecting your bias against DM. The "making a prediction" way is neutral scientific phrasing as it naturally allows for that prediction way to be wrong -- and is used even when the prediction is already known to be wrong. There's no need to force needlessly dismissive phrasing if you don't have an axe to grind.

Extraordinary claims require extraordinary evidence. Suggesting that over 80% of the matter in the universe is dark matter is a pretty extraordinary claim. The evidence is "galaxies do not appear to behave properly according to our models". However, that evidence is not evidence of dark matter, but evidence that our calculations are wrong for some reason. Dark matter is one possible solution to that problem. Another is that our understanding of gravity is incorrect on galactic scales.

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Giant hairy bollocks! There are many predictions that can be made using Dark Matter. One example, we could use it to predict that in some circumstances the Dark Matter and normal matter in a galaxy could become separated, and this has been observed. We could also use it to predict how the large-scale structure formation of the galaxy would be affected, and the observations also match this prediction extremely well; ridiculously well if you compare to the DM-free predictions.

Incorrect. This is the exact opposite of what happened. What happened was "Hey, we're observing gravitational lensing which is not congruent with the luminous matter in the galaxy", leading to "hey, maybe dark matter can get seperated from its galaxy." This is an explanation, not a prediction. It is probably the single best bit of evidence for dark matter actually existing though.

On the other hand, the universal models are much less impressive than you believe. Its called "fudging", which is the reason why dark matter stinks.

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I don't think you actually understand the reason why a comparison to epicycles is considered a bad thing. Epicycles were a case where, because they were used to explain how you could get ellipses from circles, they was no difference at all, ever between them and actual ellipses. Surely you can see how General Relativity being correct and Dark Matter being real, versus our theory of gravity being wrong, makes a difference in the resulting predictions. Or maybe not? So let's forget DM a second.

The problem with epicycles is that they were a very complicated means of pretending that the Earth was the center of the universe, compensating for flaws in the geocentric model to make observations match predictions, when the correct thing was to switch to a heliocentric model. THis is much the same - you are saying "Well, clearly dark matter exists!" when of course the alternative is to change your calculations so that gravity works differently.

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Prove me wrong. Show me you understand, by explaining to me how the prediction of Neptune's existence was or was not like epicycles.

A more apt comparison is Vulcan, the planet posited to exist inside of Mercury's orbit because its orbit did not match the calculated orbit. The actual cause was that Newton was wrong.

Basically, those required stars to get there, and we've found evidence of dark matter where there are no stars, and that it influenced the evolution of the Universe before there were stars. WIMPs could do that; MACHOs couldn't.